Chips with hermetically sealed but openable chambers

ABSTRACT

Embodiments generally relate to chips containing one or more hermetically sealed chambers that may be dismantled under controlled conditions using a release technique. In one embodiment a chip comprises a first hermetic seal bonding first and second elements to create a first chamber and a second hermetic seal bonding third and fourth elements to create a second chamber encompassing the first chamber. The first hermetic seal may be broken open independently of the second hermetic seal by the application of a mechanical or thermal technique.

RELATED APPLICATIONS

This application is related to U.S. application Ser. No. 13/291,956,filed Nov. 8, 2011, published as U.S. Patent Publication No.2013/0112650, which is incorporated herein in its entirety by reference.This application is a division of U.S. patent application Ser. No.14/270,265, entitled “Methods to form and to dismantle hermeticallysealed chambers”, filed on May 5, 2014, which is hereby incorporated byreference, as if set forth in full in this specification.

BACKGROUND

Methods of storing, inserting, or managing fluids on a microfluidic chipcurrently rely either on an external reservoir, such as a syringe, fromwhich the fluids may be delivered through a connecting assembly, such asa Luer adapter, or on the use of an on-chip reservoir such as a “blisterpack”, similar to the macro-scale versions used for packaging anddispensing drugs. The main disadvantages of the former approach includethe relatively large footprint and operational inconvenience of thedevices. The disadvantages of the latter approach typically includechemical incompatibility issues with the fluids, especially if theblister pack is made of a polymer and adhesives are used to create theseal, poor hermeticity of adhesive or gasket clamping, and poor controlof the method of releasing the fluid when required.

Similar considerations apply to managing materials other than fluidsthat may need to be encapsulated on a chip, examples including materialscomprising sensitive electronics, radioactive substances, medicalradioactive substances, biological agents, etc.

It is therefore desirable to provide a method for creating hermeticallysealed encapsulations or chambers for materials on chips that avoids theuse of polymers or adhesives, and can be easily integrated with themicrofabrication techniques used to create those chips, where the bondor bonds forming the encapsulations can be conveniently and controllablyopened, broken, taken apart or un-sealed, as and when required. It isadditionally desirable to provide a method for achieving the controlledrelease or exposure of the encapsulated materials as and when required.The chips may be microfluidic chips or flow cells.

In this disclosure, the terms “open”, “break”, “take apart” “unseal”,“unbond”, “cleave” and variants thereof are used to a large extentinterchangeably, and are defined as referring to the deliberatedismantling of a bond formed between two elements of the chip inquestion, where the dismantling may involve a break at the bondinterface within the material making up the bond itself, or a break inthe bulk material of one or both of the chip elements immediatelyadjacent to the bond interface. The word “seal” as used throughout thedisclosure is defined to mean the bond joint or bond interface where twosubstrates are fused together, for example by a room temperature laserbonding process, or fusion welding process, or using a low temperatureglass frit bonding process.

SUMMARY

The present invention includes a method for forming a hermeticallysealed chamber, the method comprising using room temperature laserbonding to create a hermetic seal between a first element and a secondelement to form the chamber. A bond interface of the hermetic seal isconfigured to allow the hermetic seal to be opened under controlledconditions using a release technique.

In one aspect, the chamber is formed within a chip. In another aspect,the chip is a microfluidic chip comprising a via connected to thechamber, wherein the chamber is configured to hold a fluid.

In yet another aspect, the release technique comprises a mechanicaltechnique that creates sufficient tensile or shear force at the bondinterface to overcome the strength of the bond interface.

In one aspect, a chip comprises a first hermetic seal bonding a firstelement and a second element to create a first chamber; and a secondhermetic seal bonding a third element and a fourth element to create asecond chamber encompassing the first chamber. The first hermetic sealmay be broken open independently of the second hermetic seal by amechanical or thermal technique.

In another aspect, an apparatus facilitating the opening of ahermetically sealed chamber included in a device comprises a fixtureconfigured to hold the device, and a system configured to createsufficient tensile or shear stress at the bond interface to open a bondinterface of the hermetically sealed chamber.

In another aspect, a method for opening a hermetic seal between a firstelement and a second element forming a chamber comprises using a releasetechnique that creates sufficient tensile or shear stress at a bondinterface of the hermetic seal of the chamber to open the hermetic seal.The release technique comprises introducing a tool to the vicinity ofthe bond interface without any contact occurring between the tool andany material within the chamber, and the breaking of the hermetic sealresults in the complete separation of the first and second elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of process steps for forming a hermetically sealedchamber according to one embodiment.

FIG. 2 illustrates three views A, B, and C of a chip fabricated toinclude a hermetically sealed chamber according to one embodiment.

FIG. 3 illustrates two views A and B of a microfluidic chip or flow cellfabricated to include a hermetically sealed chamber and vias accordingto one embodiment.

FIG. 4 illustrates a method of breaking open a hermetic seal around anon-chip chamber according to one embodiment.

FIG. 5 illustrates an apparatus that facilitates the opening of anon-chip hermetic seal according to one embodiment.

FIG. 6 illustrates a method of breaking open a hermetic seal around anon-chip chamber according to one embodiment.

FIG. 7 illustrates a method of breaking open a hermetic seal around anon-chip chamber according to another embodiment.

FIG. 8 illustrates a method of breaking open a hermetic seal around anon-chip chamber according to yet another embodiment.

FIG. 9 illustrates an apparatus that facilitates the opening of ahermetic seal around an on-chip chamber according to one embodiment.

FIG. 10 illustrates chips including features that facilitate the openingof the hermetic seal according to three related embodiments A, B and C.

FIG. 11 illustrates a chip including features that facilitate theopening of the hermetic seal according to one embodiment.

FIG. 12 illustrates an apparatus for unbonding the hermetic seal in thechip of FIG. 11 according to one embodiment.

FIG. 13 illustrates a microfluidic chip with primary and secondarychambers that can be opened according to some embodiments.

FIG. 14 illustrates a multi-substrate microfluidic flow cell includingan internal chamber according to one embodiment.

FIG. 15 illustrates a multi-substrate microfluidic flow cell includingan internal chamber according to another embodiment.

DETAILED DESCRIPTION

The manner in which the present invention provides its advantages can bemore easily understood with reference to FIGS. 1 through 15.

FIG. 1 is a flowchart of process steps for a method 100 of hermeticallyencapsulating a material on a chip according to one embodiment of thepresent invention. At step 102 a heat absorption layer is applied to anarea of the top surface of a first element of a chip, the area includingan area that bounds an open cavity. The first element may be the bottomsubstrate of the chip, or an internal substrate forming, for example, ashelf suspected above the bottom substrate of the chip. The firstelement may be made of glass or another substance that is selected forits chemical inertness with respect to the material to be encapsulatedand for its suitability for the room temperature laser bonding techniqueto be described below. U.S. Patent Publication No. 2013/0112650referenced above discussed many materials that may be suitable choicesin this latter regard.

At step 104, the material to be encapsulated is introduced to thecavity. At step 106 a second element is placed in contact with the firstelement at the desired bonding region such that the cavity is closed,forming a chamber. The second element may be the top cover of the chipor an internal cover to be covered in turn at a later stage of chipfabrication. The second element may be made of glass or another suitablyinert substance. At step 108, the first and second elements are clampedtogether in a fixture that may be partially transparent. At step 110, alaser is focused through the first or second element on the desiredbonding region. At step 112, laser energy is applied to the desiredbonding region to form a hermetic seal around the chamber, enclosing thematerial.

In some embodiments, where the chip is a flow cell, step 104 may beomitted and step 114 carried out instead, so that the chamber formed bythe seal does not initially contain the material of interest, but thematerial is introduced at a later time, making use of at least one inletvia connected to the chamber. In such a case, the material may beintroduced to the chamber subsequently, from another region of the flowcell.

Full details of the technique of room temperature laser bonding that isused in method 100 (implicit in steps 102 and 106-112) are disclosed inpatent publication 2013/0112650, referenced above. The advantages ofroom temperature laser bonding most relevant to the present inventionarise from its ability to create hermetic seals between elementscomprising relatively inert materials such as glass, without theimposition of high temperatures. Such features are clearly desirable forchambers designed to hold fluids, and also if the material to beencapsulated includes biological material such as living cell cultures.

In some embodiments, instead of step 102 as described above, the heatabsorption layer may be applied to an area of the facing surface of thesecond element before it is placed in contact with the first element,forming the chamber. Steps 104 through 112 (or steps 106 through 114)described above are carried out as before.

FIG. 2 illustrates a chip 200 fabricated to include a hermeticallysealed chamber according to one embodiment. FIG. 2A shows a view of theentire chip, FIG. 2B shows a cross-section view through its thickness,and FIG. 2C shows a cross section view that omits part of the topsubstrate 206 to more clearly reveal the inner structure. Chip 200includes a chamber 202 etched or otherwise formed into the top surfaceof bottom substrate 204. In the case shown, the chamber takes the formof a simple, roughly oval shape, occupying most of the surface of thechip, with a roughly rectangular cross section, but numerous differentshapes and sizes may be envisaged. Top substrate 206 is bonded to bottomsubstrate 204 with one hermetic seal 208 bounding the chamber 202 andanother seal 210, which may be hermetic but need not necessarily be so,bounding the perimeter of chip 200.

It should be noted that the dimensions of seals in FIG. 2 and otherFigures in this disclosure are not to be taken as being “to scale”,their thicknesses and widths being greatly exaggerated with respect totheir length for clarity. Similarly, the thicknesses of the gaps betweenbonded substrates shown in these Figures have been greatly exaggeratedfor clarity. In reality, the substrates are in intimate contact witheach other when bonded, and any gap is extremely small, if discernableat all.

While many of the embodiments discussed and illustrated in thisdisclosure concern chambers with dimensions of the order of microns,millimeters or centimeters, fabricated in chips of corresponding size,it is envisaged that the methods and systems described could bebeneficially applied to macro-scale devices such as cuvettes, or tanksthat could have dimensions of the order of meters.

FIG. 3 is a cut-away view of a chip 300, fabricated according to anotherembodiment. FIG. 3A shows a view of the entire chip, and FIG. 3B shows aview that omits part of the top substrate 306 to more clearly reveal theinner structure. Chip 300 has one hermetic seal 308 around chamber 302and another hermetic seal 310 near the chip edges. In this flow cellembodiment, chamber 302 is shaped as a relatively narrow channel withrounded ends, and top substrate 306 includes two vias 312 at these endsto permit external connections to be made for the passage of a fluidinto or out of the chamber. In some embodiments, vias may be present inbottom substrate 304 additionally or instead of top substrate 306. Insome embodiments there may be only one via, or more than two.

In the embodiment shown in FIGS. 1 and 2, two separate seals arepresent. In some embodiments, there may be only one seal bounding thechamber, that one seal being hermetic.

FIG. 4 illustrates a method of breaking open a hermetic seal 410,previously formed around encapsulated material, or around an emptycavity in a flow cell, by a method such as method 100, according to afirst embodiment. A tool 412, typically one with a fine edge or a tippedpoint as shown, is inserted between the portions of the sealed first andsecond elements 414, 416 that slightly project beyond seal 418, at orvery close to bond interface 420. A controlled mechanical force isapplied by tool 412 to create sufficient tensile stress at bondinterface 420 of seal 418 and in turn at bond interface 422 of hermeticseal 410 to overcome the strength of both seals. In some cases, hermeticseal 410 may be the only seal present.

In some embodiments, the tool may be moved relative to the chip totraverse a portion of or the entire perimeter of the seal around thechamber or chip. The tool may be operated in a simple manual fashion orwith the use of an apparatus, not shown, designed to more convenientlyapply the necessary mechanical force. In some embodiments, such anapparatus includes a fixture in which the chip is held, and an actuationmechanism which when actuated will position one or more tools at or inthe vicinity of the bond interface and move them in a controlled path tobreak through the seal. In some embodiments, it may not be necessary tomove the tool after placing it in position. In some embodiments, thebreaking of the seal by manual or other means results in the completeseparation of elements 414 and 416. If elements 414 and 416 are the topand bottom substrates of a chip, the entire chip may be cleanlyseparated into two parts enabling access or recovery of the contents ofthe chip.

One example of a suitable tool 412 is a razor blade. Other examplesinclude wedges or other knife-like tools. In some embodiments, the toolmay be operated, manually or in combination with an apparatus asdescribed above, to apply a shear stress rather than a tensile stress toachieve the same objective of breaking open the hermetic seal. In someembodiments, the tool may be operated to cause the unbonding of thehermetic seal without any contact occurring between the tool and anymaterial within the chamber.

FIG. 5 illustrates one embodiment of a simple apparatus, essentially afixture 502, including a cavity 504 into which the chip 500 to beunsealed is inserted, and an opening, shown at the front right edge ofthe Figure, precisely shaped to accept a razor blade 506 and positionedso that the blade 506 can be inserted at a suitable position to stressand break the hermetic seal of interest in the chip.

FIG. 6 illustrates a method of breaking open a hermetic seal 610,previously formed around encapsulated material by a method such asmethod 100, according to one embodiment. The sealed chip is coupled to afixture 620 such that a neutral axis X is located at a predetermineddistance from the “bond line” characterizing seal 610. A preciselycontrolled force, low enough to avoid the risk of breaking the bulkmaterial of the chip, but high enough to cause the required shear stressat the bond line to break the seal open, is then applied to the chip. Inthe embodiment illustrated, the force is applied orthogonally to theplane of the seal, causing the chip to bend as indicated schematicallyin the Figure inset. In some embodiments, the bending may be carried outwithout the aid of a fixture, but precise control may be more difficultto achieve.

FIG. 7 illustrates a method of breaking open a hermetic seal, previouslyformed around encapsulated material or flow cell by a method such asmethod 100, according to another embodiment. Opposing ends of chip 700are twisted in opposite directions as indicated by the curved arrows.Such twisting motion causes shear stresses at seal 710. The directionsof the twist may be reversed, and the to and fro twist cycle repeated asnecessary until the seal is opened. In some embodiments the twisting iscarried out manually. In some embodiments a fixture or other apparatusmay be used instead of or in addition to manual twisting.

FIG. 8 illustrates a method of breaking open a hermetic seal, previouslyformed around encapsulated material or flow cell by a method such asmethod 100, according to yet another embodiment. In this embodiment, athermal technique is employed. Thermal techniques may be used when thetwo chip elements that have been bonded, or other elements coupled tothose bonded elements, have been selected to have coefficients ofthermal expansion (CTEs) that differ by a predetermined amount. Inresponse to a thermal change, (typically the application of heat) thedimensions of these elements will change at rates sufficiently differentto cause shear stress at the bond interface that results in the breakingof the seal. In the case illustrated, in response to the application ofheat, top substrate 810 expands more than bottom substrate 820, clearlyputting shear stress on seal 830 between the two substrates.

In some embodiments, the heat is applied with a source ofelectromagnetic radiant energy, such as an infrared (IR) beam. Theradiant energy may be applied in a diffuse or localized, directedmanner. In some embodiments a chip fixturing and laser translationsystem similar to those systems used to carry out room temperature laserbonding may be used to apply the laser energy with precise control to“unbond” seals rather than creating seals. FIG. 9 shows one example ofan apparatus of this sort. The chip to be unsealed (not shown) would bepositioned on the x-y stage 850 and a laser beam would be guided thoughthe optical system to focus on the chip at the bond interface ofinterest. Translating the chip and/or the beam allows the length of aseal to be tracked, or a series of sealed sites over the surface of thechip to be addressed as desired. In some embodiments, where the piece tobe unbonded remains stationary the laser beam can traverse the chipthrough the use of moving mirrors in a scanner system. In otherembodiments, a combination of stage movement and laser scanning can beemployed.

In some embodiments, the heat may be applied by a more conventionalheating element, using conduction or convection. In one embodiment ofthis bond “disassembly” method, electrical resistance heating may beused to separate the bond. The heat absorption layer, typically a thinmetal film, used to create the bond, can also be used as a conductivelead, and patterned as necessary around the bond line, such that passingan electric current through the lead creates localized resistive heatingwhich cleaves the bond.

FIGS. 10 and 11 relate to methods of breaking open a hermetic seal,previously formed around encapsulated material on a chip or flow cell bya method such as method 100, according to yet other embodiments. Inthese cases, generally involving mechanical techniques such as thosedescribed above with respect to the embodiments illustrated in FIGS. 4through 7, the breaking of the seal is facilitated by the presence ofstructural features deliberately included in the chip for that purpose.

In the embodiment illustrated in FIG. 10A, the feature in question is anintentional longitudinal alignment offset in the two bonded elements ofthe chip, which makes it easy to apply an opposing force to thesubstrates (typically by compression or squeezing as indicated by theopposing arrows) which generates a shear stress sufficient to cleave thebonds. In the embodiments of FIGS. 10B and 10C, the alignment offsetsare lateral and tilt/skew respectively. In the former case, simplycompressing the chip by applying lateral force at two opposing positionsas indicated by the arrows causes sufficient shear stress to cleave thebond; in the latter case, applying compressive lateral force at bothends of the chip causes sufficient shear stress to cleave the bond.

FIG. 11 illustrates a chip 900 into which the features facilitating bonddisassembly are undercuts. Four undercuts 910 have been fabricated intothe top substrate 920. Each undercut is angled inward, having a largeropening on the outer edge of the chip converging to a smaller opening asit approaches the bond interface 930 of the outer seal. The purpose ofthe undercuts is to make it easy to insert a tool directly in afavorable position and orientation to stress that bond interface, and,in the case shown, the bond interface of the inner seal in its turn. Inother embodiments, similar undercut features may be fabricated into thebottom substrate instead of or in addition to the top substrate. In someembodiments, the undercuts may have shapes other than the angled wedgesshown. In some embodiments the undercuts may have shapes designed toaccommodate a particular tool or type of tool. In one embodiment, thechip feature facilitating bond disassembly is a chamfer, extendingaround the entire perimeter of the chip.

FIG. 12 illustrates one embodiment of an apparatus that can be used forunbonding hermetic seals in a chip such as chip 900, having undercutfeatures 910, using a fixture 950 including a cavity 960 into which thechip to be unsealed (shown in FIG. 12C) may be inserted. FIG. 12A is aview of the fixture prior to the insertion of the chip, showing tools970 in a retracted position. FIG. 12B shows tools 970 in an extendedposition, in response to a user pressing button 980. FIG. 12C is a viewof the fixture after chip 900 has been inserted into cavity 960.Pressing button 980 with the chip in place as shown causes tools 970 toengage with undercuts 910, creating stress at multiple positionssimultaneously around the perimeter of the sealed chip, resulting in theunbonding of the seal or seals.

The embodiments disclosed above have been generally described, for thesake of simplicity, in terms of a seal that bonds two parts of a chiptogether around an encapsulated material such that when the seal issubsequently broken, the chip is cleaved in two, exposing the enclosedmaterial. However, in some embodiments, the methods and aspects of thepresent invention may be applied with respect to forming and opening oneor more encapsulation chambers within a multi-substrate chip. In suchcases, an individual chamber or reservoir can be opened independently ofthe opening of any other chamber on the chip, and independently of thebond sealing the two external substrates together.

In some microfluidic chip embodiments, for example, an encapsulationchamber may be a reservoir containing a fluid (which can be underpressure) or any other type of reagent that can be released into achannel connecting the chamber to another portion of the chip. Thereleased material may then be subjected to a mixing process, and/oradded to another released fluid. It may be directed to flow in apredetermined direction to another portion of the chip. In suchembodiments, the material release mechanism can be any of the mechanicalor thermal techniques described previously.

FIG. 13 illustrates a microfluidic chip having a primary chamber 130, asecondary chamber 132, and a channel 134 in an intermediate position.According to one embodiment, seal 136 between secondary chamber 132 andchannel 134 may be broken by increasing the temperature of fluidencapsulated in secondary chamber 132, Thermal expansion then increasesthe fluid pressure and forces the fluid to break through seal 136 andenter channel 134. A very small opening may be made in seal 138 betweenprimary chamber 130 and channel 134 using a thermal technique, forexample by using a focused laser beam. Alternately, pressure exerted onseal 138 from the pressurized fluid forced out of the secondary chamber132 may create the desired opening. In either if these two cases, anopening may be created that is large enough to allow fluid from primarychamber 130 to enter channel 134, but small enough to ensure that thatpassage of fluid only occurs in response to deliberately increasedpressure from within the primary chamber. In other words, the openedseal 138 may act as a valve, allowing fluid previously encapsulatedwithin the main chamber to be “dispensed” in controlled doses byapplying pressure to the primary chamber.

FIG. 14 illustrates a multi-substrate chip according to one embodiment.Microfluidic chip 150 includes a top substrate 155 and a bottomsubstrate 160 bonded at hermetic seal 165 to define a chip interiorvolume. Chip 150 also includes an inner substrate 170 bonded at hermeticseal 175 to raised features on bottom substrate 160 to define a chambercontaining fluid 180. Seal 175 can be broken in a controlled fashionwhen required, allowing fluid 180 to be released from the chamber,possibly by capillary action or bulk pressure-driven flow, while seal165 may remain intact, protecting the contents of chip 150 from theexternal environment. Substrates 155 and 160, and 170 typically compriseglass, but may comprise any other material that is chemically inert withrespect to fluid 180. This chemical stability coupled with thehermeticity and mechanical robustness of the seals makes suchembodiments of the current invention particularly desirable.

FIG. 15 illustrates a multi-substrate microfluidic chip 151 according toanother embodiment. This differs from chip 150 in having its innersubstrate 171 bonded in a bent configuration at hermetic seal 176 tobottom substrate 161. This “locked-in” bend means that energy is trappedin substrate 171, held in check by the strength of the seal, but whenthe seal is opened, using any of the techniques discussed above,substrate 171 will “spring” away from its bound position, allowing fluid181 an easy exit from the chamber into surrounding portions of the chip.

In some embodiments, a multi-substrate chip may include one hermeticallysealed outer chamber that encapsulates more than one hermetically sealedinner chamber. The seals of each may be independently broken open as andwhen desired using any of the release techniques described above,allowing, for example, material enclosed within one chamber to bereleased into a flow channel, to undergo some process, and then to flowinto a second chamber containing other material so that mixing occurs.In such an example, it may be desirable to subsequently unbond a sealbetween the second chamber and another channel of the chip, and so on.Finally, the hermetic seal of the outer chamber may be opened up toallow access to all the encapsulated materials.

Embodiments described herein provide various benefits. In particular,embodiments provide for the room temperature formation of hermeticseals, forming compact, chemically inert enclosures for materials withinchips, while ensuring that those materials may be subsequently accessed,released, or otherwise managed on the chip, by the carefully controlledbreaking of one or more seals. These benefits may be especially valuablein applications where sensitive biological materials are involved.

The above-described embodiments should be considered as examples of thepresent invention, rather than as limiting the scope of the invention.Various modifications of the above-described embodiments of the presentinvention will become apparent to those skilled in the art from theforegoing description and accompanying drawings. Accordingly, thepresent invention is to be limited solely by the scope of the followingclaims.

The invention claimed is:
 1. A chip comprising: a first hermetic seal bonding a first element and a second element to create a first inner chamber; and a second hermetic seal bonding a third element and a fourth element to create a second outer chamber encapsulating the first inner chamber; wherein the first hermetic seal is configured to be broken open independently of the second hermetic seal by the application of a mechanical or thermal technique.
 2. The chip of claim 1 wherein the chip is a microfluidic chip and the first chamber is configured to hold a fluid.
 3. The chip of claim 2 further comprising a via connected to the first chamber.
 4. A microfluidic chip comprising: a first hermetic seal bonding a first element and a second element to create a first chamber configured to hold a fluid; and a second hermetic seal bonding a third element and a fourth element to create a second chamber encompassing the first chamber; wherein the first hermetic seal is configured to be broken open independently of the second hermetic seal by the application of a mechanical or thermal technique; and wherein the first hermetic seal holds the first element in a bent configuration such that if the first hermetic seal is broken to form an opening in the first chamber, mechanical energy within the first element is released, increasing the size of the opening such that the fluid may easily exit the first chamber.
 5. A microfluidic chip comprising: a hermetic seal bonding a first element and a second element to create a chamber within the chip, the chamber being configured to hold a fluid; wherein the hermetic seal is configured to be broken open under controlled conditions using a release technique; and wherein the structural feature comprises an undercut at or in close proximity to the bond interface, the undercut configured to accept the insertion of a tool to break open the hermetic seal.
 6. A microfluidic chip comprising: a hermetic seal bonding a first element and a second element to create a chamber within the chip, the chamber being configured to hold a fluid; wherein the hermetic seal is configured to be broken open under controlled conditions using a release technique; and wherein the first element is characterized by a first coefficient of expansion and the second element is characterized by a second coefficient of expansion different from the first such that in response to a thermal change, the dimensions of these elements will change at rates sufficiently different to cause shear stress at the bond interface that results in the breaking of the hermetic seal. 